1. Field of the Invention
This invention relates to a biomedical article made of alumina ceramics and, more particularly, to an alumina ceramics biomedical article having a high strength and an excellent slidability.
2. Description of the Prior Art
As artificial bone members such as artificial hip joint, there have been known an artificial hip joint comprising a combination of a polymer material (e.g., ultra-high molecular weight polyethylene). However, there has been the problem that the long use of the socket made of ultra-high molecular weight polyethylene in the living body causes a wear of the socket, resulting in a displacement between the implanted artificial bones and the natural bones in the living body due to wear powder. Also, wear powder of metal has been worried to give adverse influence to the living body. Further, zirconia ceramics is subject to crystalline phase transference phenomenon in a long use, consequently lowering the mechanical strength.
To solve these problems, a variety of research and development about artificial bone members have been made. As an example, use of alumina ceramics has been proposed because of harmless to the human body.
Japanese Laid Open Patent Application No. 51-67693 discloses a stem head made of alumina ceramics comprising an aluminum oxide having a purity of not less than 99.7% by weight, a density of not less than 3.90 g/cm.sup.3, and an average crystal grain size of not more than 10 .mu.m. This artificial bone member can reduce the wear of a socket made of ultra-high molecular weight polyethylene. However, its mechanical strength is insufficient.
Japanese Patent No. 2579212 discloses a stem head made of polycrystalline alumina ceramics comprising an aluminum oxide having a purity of from 99.5 to 99.9% by weight and an oxide of at least one selected from the group consisting of Mg, Ca, Ba, Sr, Sc, Y, La and Ce as sintering agent. Also, Japanese Patent Publication No. 7-94344 discloses a stem head made of polycrystalline alumina ceramics comprising an aluminum oxide having a purity of not less than 99.9% by weight and an oxide of at least one selected from the group consisting of Mg, Ca, Ba, Sr, Sc, Y, La and Ce as sintering agent.
However, these known artificial bone members have the following problems. The alumina ceramics constituting the artificial bone member include the sintering agent. The sintering agent causes glassy grain boundary layers in a sintered body, accordingly making it impossible to raise the three-point bending strength of the alumina ceramics more than 640 MPa, which is considerably lower than zirconia ceramics having a strength of about 1200 MPa. Accordingly, the artificial bone member made of such alumina ceramics is likely to break or fracture in the living body.
On the other hand, reducing the addition of sintering agent involves a poor dispersion of sintering agent, resulting in partial crystal grain size increases because of insufficient deterrent to crystal grain growth, and thus irregularities in the crystal grain size of the sintered body. Consequently, the mechanical strength of the alumina ceramics lowers.
The artificial bone member made of alumina ceramics has an improved slidability to a socket made of ultra-high molecular weight polyethylene. From the viewpoint of reduction or elimination of wear powder, it could be thought to be advantageous to combine an artificial joint made of ceramics and an artificial socket made of ceramics because of the high hardness of ceramics. However, there have never been raised any technical proposals of improved alumina ceramics having excellent slidability especially at a ceramics to ceramics interface to take such advantageous effect of alumina ceramics. This subject demands close investigation for biomedical articles.